1. Field of the Invention
The present invention relates to an illuminating device, and a display device and a television receiver that have the illuminating device. More particularly, the present invention relates to an illuminating device provided with a light source, and a display device and a television receiver having the illuminating device.
2. Description of the Related Art
Conventionally, as illuminating devices, backlight units used in display devices (such as television receivers) have been known (see, for example, JP-A-2005-285620).
FIG. 7 is a diagram schematically showing an example of the structure of a liquid crystal display device (display device) in which a conventional backlight unit (illuminating device) is used. As shown in FIG. 7, a liquid crystal display device (display device) using a conventional backlight unit (illuminating device) 110 is used in a state in which the backlight unit 110 is disposed on the rear surface side of a liquid crystal display panel 120. The conventional backlight unit 110 is so designed as to irradiate the liquid crystal display panel 120 with planar light from the rear surface side of the liquid crystal display panel 120. Hereinafter, a description will be given of the structure of the conventional backlight unit.
The conventional backlight unit (illuminating device) 110 is provided at least with a reflection sheet 101, a plurality of fluorescent lamps 102 forming a light source, and a diffusion plate 103. The reflection sheet 101 is disposed so as to cover the plurality of fluorescent lamps 102 from the rear surface side. The reflection sheet 101 has a function of reflecting light from the plurality of fluorescent lamps 102 toward the front surface side.
The plurality of fluorescent lamps 102 are each disposed to extend in a direction perpendicular to the paper plane of FIG. 7. Furthermore, the plurality of fluorescent lamps 102 are arranged at predetermined intervals in a direction perpendicular to the direction in which the fluorescent lamps 102 extend (the right-left direction in FIG. 7). It is by the plurality of fluorescent lamps 102 that light which is to be emitted from the backlight unit 110 is generated.
The diffusion plate 103 is disposed at a predetermined distance from the fluorescent lamps 102 so as to cover the plurality of fluorescent lamps 102 from the front surface side. The diffusion plate 103 has a function of making images of the fluorescent lamps 102 invisible by diffusing the light from the plurality of fluorescent lamps 102.
In the conventional backlight unit 110 shown in FIG. 7, in order to make the images of the fluorescent lamps 102 invisible, the ratio (B/A) of distance A (the distance from the centers of the fluorescent lamps 102 to the rear surface of the diffusion plate 103) to distance B (the distance between the centers of adjacent ones of the fluorescent lamps 102) needs to be large to some extent. In other words, in order to make the images of the fluorescent lamps 102 invisible to secure even brightness, distance A (the distance from the centers of the fluorescent lamps 102 to the rear surface of the diffusion plate 103) needs to be large to some extent. As a result, inconveniently, in the conventional backlight unit 110 shown in FIG. 7, it is difficult to reduce distance A (the distance from the centers of the fluorescent lamps 102 to the rear surface of the diffusion plate 103) to achieve thinness.
A conventionally proposed solution for coping with this inconvenience is a backlight unit in which a light guide plate is used to reduce its thickness.
FIG. 8 is a diagram schematically showing an example of the structure of the just-mentioned conventionally proposed backlight unit. As shown in FIG. 8, the conventionally proposed backlight unit 130 is provided at least with a plurality of fluorescent lamps 111, a plurality of light guide plates 112 each making a pair with a corresponding one of the fluorescent lamps 111, and a diffusion plate 113. The plurality of fluorescent lamps 111 are each disposed to extend in a direction perpendicular to the paper plane of the figure, and also, they are arranged at predetermined intervals in a direction perpendicular to the direction in which the fluorescent lamps 111 extend (the right-left direction in FIG. 8).
The plurality of light guide plates 112 each have a light entrance surface 112a formed as a predetermined side surface, and are formed in the shape of a wedge that is progressively thinner farther away from the light entrance surface 112a. The plurality of light guide plates 112 are arranged in the direction in which the fluorescent lamps 111 are arranged (the right-left direction in FIG. 8) without a gap, such that the light entrance surface 112a of each of the light guide plate 112 faces a corresponding one of the fluorescent lamps 111.
The plurality of light guide plates 112 each have a light exit surface 112b formed as its front surface. The diffusion plate 113 is disposed so as to cover the light exit surfaces 112b of the plurality of light guide plate 112 from the front surface side.
Incidentally, a conventional backlight unit 130 shown in FIG. 8 is, like the conventional backlight unit 110 shown in FIG. 7, used in a state in which it is disposed on the rear surface side of the liquid crystal display panel 120.
With the conventional backlight unit 130 shown in FIG. 8, since light from each of the plurality of fluorescent lamps 111 is guided to the diffusion plate 113 after being diffused by the corresponding one of the light guide plates 112, it is possible to make the images of the fluorescent lamps 111 invisible even when distance A (the distance from the centers of the fluorescent lamps 111 to the rear surface of the diffusion plate 113) is reduced.
However, although the images of the fluorescent lamps 111 can be made invisible with the conventional backlight unit 130 shown in FIG. 8, there arises another inconvenience that brightness is high at connection portions 112c that are each a portion between adjacent light guide plates 112. Thus, when the conventional backlight unit 130 is used in a state in which distance A (the distance from the centers of the fluorescent lamps 111 to the rear surface of the diffusion plate 113) is reduced, it is difficult to obtain even brightness that is required of backlight units for liquid crystal display devices. That is, it is disadvantageously difficult to improve the evenness of the brightness of the conventional backlight unit 130 while reducing its thickness.
Furthermore, the conventional backlight unit 130 shown in FIG. 8 is disadvantageous in that the plurality of light guide plates 112 used therein make the backlight unit 130 heavier due to their respective weights. Moreover, the conventional backlight unit 130 shown in FIG. 8 is disadvantageous in that the light guide plates 112 absorb light, and this degrades the light use efficiency.